Electromagnetic pumping apparatus for use in electrophotography



Sept. 30, 1969 R. G. OLDEN 3,459,911

ELECTROMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY FiledJan. 30, 1967 3 Sheets-Sheet 1 O W Y j; /4 I 16 '25 [I I I M v A/ro,e Wi6 0w,

P 0, 1969 R. s. OLDEN 3,469,911

ELECTROMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY FiledJan. 30, 1967 3 Sheets-Sheet 2 q I 14 u E 12 I 1 Q g I] X 5 g1! 41 1 2 Ia j I I v v j I I m Fig I h I A I v Z4 1 IOQOO O'OOOI Sept. 30, 1969 R.G. OLDEN 3,469,911

ELECTROMAGNETIC PUMPING APPARATUS FOR USE IN ELECTROPHOTOGRAPHY FiledJan. 30, 1967 3 Sheets-Sheet 3 v Mum/r52" v ,ggv' m/. 51 4 iaeu'r'United States Patent 3,469,911 ELECTRQMAGNETIC PUMPING APPARATUS FOR USEIN ELECTROPHOTOGRAPHY Roger G. Olden, Princeton, N.J., assignor to RCACorporation, a corporation of Delaware Filed Jan. 30, 1967, Scr. No.612,684 Int. Cl. G03g 15/02 US. Cl. 355-3 1 Claim ABSTRACT OF THEDISCLOSURE An electromagnetic pumping apparatus for transporting apowdered developer of iron and toner particles from a reservoir to adeveloping station in an electrostatic printing machine. The pumpcomprises a thin-walled tube of nonmagnetic material surrounded by anumber of electric coils which are energized in sequence. As the coilsare sequentially energized the developer is caused to move along thetube, from the reservoir to the developing station. The switching devicethat energizes the coils is such that two adjacent coils are alwaysenergized at any particular time and the last coil in the sequence isenergized for a period shorter than that of the other coils.

Background of the invention This invention relates generally to improvedmeans for circulating a magnetic developer material through anelectrostatic printing machine or the like, and more particularly toimproved apparatus for conveying magnetic developer material from areservoir to a developing station in such machines.

In electrophotography it is common to apply a uniform electrostaticcharge to the surface of a photoconductive layer. The charge on selectedareas is then dissipated by exposing the surface to a light image.Finely divided developer particles which adhere to the charged areas ofthe surface by electrostatic attraction are applied to the resultingpattern of charges, rendering the pattern visible. A magnetic brushincluding a mixture of magnetic carrier particles and nonmagneticdeveloper particles is a con- Venient way to develop the electrostaticimage. Permanent visible images can be obtained, for example, by usingthermoplastic developer particles which can be heat fused to thephotoconductive layer.

The powder developer used in many electrostatic printing machinesconsists of finely divided iron particles and thermoplastic tonerparticles. Methods presently used to transport this developer from areservoir to the area where the electrostatic image is developed involvevarious problems. Mechanical conveyors cause dusty operation and consumea large amount of space. Screw feeds necessitate locating the reservoirclose to the developing area, are limited in capacity and slow machineoperation. Both of these methods of moving developer are mechanicallycomplicated and therefore present maintenance problems. A gravity feedis mechanically simpler and consumes no power but it necessitatesplacing the developer reservoir high in the machine, and such anarrangement limits the size of the reservoir. This method alsonecessitates locating the reservoir close to the developing area.

Experience has shown that clear, crisp electrostatic prints can beobtained when the electromagnetic developer is continually supplied withfresh developer material. This can be done if the magnetic developermaterial is circulated from a fairly large reservoir, and the unusedportion is returned to the reservoir to be recirculated.

Summary of the invention The invention comprises an electromagneticpumping apparatus to transport magnetic developer material from areservoir to a developing station in an electrostatic printing machineor the like. The novel magnetic pumping apparatus includes a hollow tubeof a nonmagnetic material surrounded by a plurality of electric coilsspaced along its length. When the coils are energized in succession by arotating switch, the magnetic developer material is moved along thetube. One end of the tube extends into the reservoir of developermaterial and the other end is disposed adjacent to the electromagneticdeveloping area. The magnetic pump supplies a developer mixtureconsisting of iron and toner particles to a magnetic brush which appliesthe toner particles to an electrostatic image.

In one embodiment of the invention the magnetic pump deposits thedeveloper material on a rotating brush which in turn brushes thedeveloper particles onto the electrostatic image. An electromagnetmounted behind the electrostatic image completes the magnetic developerbrush. In another embodiment the magnetic pump cascades the developermaterial directly across the electrostatic image which has anelectromagnet mounted behind it to form a magnetic developing brush.After passing through the magnetic developing brush in both embodiments,excess developer material falls back into the reservoir where it can berecirculated by the magnetic pump.

The magnetic pump involves no moving parts thereby decreasingmaintenance problems. It allows the reservoir to be placed in anyconvenient location within an electro static printing machine since itcan transport the magnetic developer material to a developing area abovethe reservoir and at any distance from it. The pumping apparatus can bebuilt with a sufiicient capacity to supply developer material at anypractical rate to the magnetic developer. Dust is kept at a minimumsince the powder developer moves through an enclosed tube. Since theinvention can raise the developer mixture to a developing area at ahigher level, gravity can be utilized to return excess developer to thereservoir allowing a circulation of the developer and the reuse of theiron particles. When a large reservoir is employed, individual particlesof developer are rested between circulations for a far greater period oftime than they are in use, so that the developer mixture is always freshat the developing area. This freshness is important in producing clean,crisp prints from an electroprinting machine.

Brief description of the drawings FIG. 1 is a cross-sectional side viewof the novel magnetic pumping apparatus with a partial schematic diagramof its accompanying electric circuit;

FIG. 2 is a cross-sectional side view of one embodiment of theinvention; and

FIG. 3 is a cross-sectional view of a second embodiment of theinvention.

Description of the preferred embodiments Referring to FIG. 1 of thedrawings the novel magnetic pumping apparatus 8 comprises a thin-walledtube 10 of nonmagnetic material surrounded by a number of coils, such ascoils 12, 14 and 16. The intake end 18 of the tube 10 extends into areservoir 20 of magnetic developer material. The exhaust end 22 of tube10 is located adjacent to and in operative relation with a magneticdeveloper station. The tube '10 can be of any desired crosssectionalconfiguration.

The coils, for example coils 12, 14 and 16, are spaced equally along thelength of the tube 10. Each coil consists of a plurality of turns ofelectrically conducting wire. Spacers 24 separate the coils the desireddistance and prevent electrical contact between them. The spacers 24 areconstructed of electrically nonconducting material and may have anysuitable shape. A nonmagnetic and nonconducting housing 25 encases thecoils 12, 14 and 16, thereby preventing iron particles from coming intocontact with them. The housing 25 is a tube having a diameter which islarge enough to enclose the magnetic pump tube and its surroundingcoils. The housing has the same shape as tube 10 and is closed at ends18, 22 by a disk of nonconducting material 26 having an aperture 27 toallow access to tube 10. The coils 12, 14 etc. are completely enclosedin the space between the walls of tube 10 and housing 25.

The reservoir may be fabricated from any material having suflicientstructural strength. It can be made in any convenient shape but shouldbe large enough to hold an adequate supply of developer material 28.Magnetic pump tube 10 with its surrounding coils -12, 14 and 16 andhousing extends into reservoir 20 to a point near the bottom to insurethat all of developer material 28 is periodically circulated throughtube 10 to the remainder of the apparatus.

Coils 12, 14 and 16 are energized by a switch 30. The switch 30 has anumber of fixed switch contacts 12a, 14a, for example, arranged in acircle around the circumference of the switch. The switch contacts aresmall metallic disks having terminals to which wires 31 are attached.The wires 31 link the fixed switch contacts 12a, 14a, etc. to thecorresponding coils 12, 14, etc. that they energize. A rotating switcharm 32 is mounted on a shaft which extends through the center of theswitch 30. A rotating contact 34 is attached to the end of the switcharm 32 so that contact 34 passes across fixed switch contacts 12a, 14a,etc. Rotating contact 34 is wide enough to engage two adjacent switchcontacts, such as 12a and 14a, simulaneously. Fixed switch contact 16ais narrower than the other switch contacts 12a, 14a, etc. and is offsetfrom the circle of switch contacts and placed closer to the center ofswitch 30 so that the rotating contact 34 does not engage it. A secondrotating contact 36 is mounted on the rotating arm 32. Contact 36 islocated closer to the center shaft of the switch 30 than the rotatingcontact 34 so that it will engage fixed contact 16a. Contact 36 isnarrower than contact 34 so that fixed contact 16a is only engaged for ashort time.

A source of electrical energy is connected to the rotating switch arm 32so that the switch contacts 12a, 14a, etc. are energized as the contact34 moves across them. Electrical energy is conducted from the fixedswitch contacts through the wires 31 to the coils 12, 14, etc. When thecoil 12 is energized, a magnetic field is produced which draws a slug 40of magnetic developer material into tube 10 and holds it at the centerof the coil 12. Contact 34 on revolving arm 32 is wide enough to contacttwo adjacent switch contacts simultaneously so that the next coil ontube 10, coil 14, is energized before the magnetic field of coil 12 hascollapsed and the slug 40 moves up the tube 10toward coil 14 rather thanfalling back toward the reservoir 20. As the rotating arm 32 movesacross the other switch contacts in switch 30, the corresponding coilsare energized and the resulting magnetic fields move the slug 40 ofdeveloper along tube 10. When the narrow contact 36 on rotating arm 32engages contact 16a, coil 16, the last of the series of coils, isenergized. Since both the revolving contact 36 and the switch contact1611 are narrow, they touch for a short period of time and the coil 16is only energized momentarily so that the slug 40 does not stop withinits magnetic field but instead the slug 40 is ejected through dischargeend 22 of tube 10. The magnetic pump 8 can deliver a continuous supplyof magnetic developer material if a plurality of rotating arms are usedin the switch 30.

A magnetic pump, similar to that shown in FIG. 1, was constructed havinga tube diameter of inch and an over-all length of 8 inches. Twelve coils/2 inch in width 4 were arranged equidistantly along its length witheach coil containing approximately 2500 turns of number 35 wire. Acurrent of about .820 ma. flowed through the coils. The coils wereenergized successively by a rotating switch arm similar to that shown inFIG. 1. This device pumped a standard developer material, consisting oftoner and iron particles, well, raising it about 6 inches vertically andejecting it through a curved portion of the tubing as shown in FIG. 1.

FIG. 2 shows an embodiment of the invention which is utilized in anelectrostatic printing machine. The intake end 18 of the magnetic pump 8extends into the reservoir 20 of magnetic developer material 28. Thedischarge end 22 of the tube 10 is disposed adjacent to a rotating brush42. A trough 44 attached to the discharge end 22 of the tube 10 extendspartially around the rotating brush 42. The trough 44 is placed close tothe surface of the rotating brush 42 and conforms closely to the shapeof the brush. The cross-sectional configuration of tube 10 can be madeto correspond to the cross-sectional area of the rotating brush 42. Theshape of the entire magnetic pumping apparatus 8 is made to conform tothe space available in the electrostatic printing machine but themagnetic pumping apparatus is otherwise the same as described above inreference to FIG. 1. The brush 42 consists of a solid central disk ofsuitable material with a shaft through its center to allow rotation. Thecircumference of the brush 42 is covered with a nonconducting materialsuch as nylon velour. The brush 42 rotates at a speed about one half thespeed at which the paper 46 moves across it in the same direction as thepaper is moving.

Magnet 48 is an electromagnet which is mounted closely behind a platen50 and directly above the brush 42. The poles of magnet 48 form amagnetic developing brush with the rotating brush 42. The platen 50consists of a fiat metal plate placed between the paper 46 and theelectromagnets 48 and 51.

Brushes 52 and 54 are smaller than brush 42 but are otherwise similar inconstruction. The brush 52 rotates in a counterclockwise direction whilebrush 54 rotates clockwise in a direction opposite to the motion of thepaper. The second electromagnet 51 which is similar to magnet 48 ismounted behind the platen 50 and above brushes 52 and 54 so that itforms two additional magnetic brushes with brushes 52 and 54.

Magnetic pump 8 transports magnetic developer material 28 from thereservoir 20 and deposits it on the rotating brush 42. The trough 44prevents the developer from falling back into the reservoir 20 andcauses it to be picked up by the brush 42. As the brush rotates, thepowdered developer is brushed against the paper which has anelectrostatic image on the side facing the brush 42. The platen 50 holdsthe paper flat and insures uniform contact between the paper and therotating brush so that developer is spread across all areas of theelectrostatic image. Electromagnet 48 completes a magnetic developingbrush with rotating brush 42 and attracts the magnetic developer to thepaper 46 increasing the probability that toner particles will adhere tothe charged areas of the electrostatic image.

After the paper has passed through this first magnetic brush, themagnetic field decreases at point 58 and the excess developer is free tofall back into the reservoir 20. The rotation of brush 42 also tends toremove excess developer from the paper at the limit of the magneticfield of magnet 48. Brushes 52 and 54 perform a dual function. Togetherwith electromagnet 51 they form a second magnetic developing brush tofurther fix the image but they also serve as cleanup brushes to removeexcess developer from the paper 46. This is especially the function ofthe brush 54 which rotates in a direction opposite to that of thebrushes 42 and 52 and opposite to the direction in which the paper ismoving. Excess developer which is brushed from the page at points 60 and62 also falls back to the reservoir 20.

The invention provides a continuous circulation of developer materialthrough the electrostatic printing machine. When the reservoir 20 islarge, the time during which individual particles of developer are usedbecomes small and a supply of fresh developer is always available to themagnetic developing brush.

FIG. 3 shows a second embodiment in which the invention is utilized inan electrostatic printing machine. The electromagnetic pump is similarin construction to that described in FIG. 1. A continuous web of paper46, which has been treated with a chemical such as zinc oxide to make itphotosensitive, it passed through a corona generator 64 and is thenexposed to a light image 68. Various methods and apparatus for coronageneration and photographic exposure are known in the art and thesesteps in the electroprinting process are not part of the subjectinvention.

The paper 46 is passed around two rollers 70 and 72. These rollers arecylinders constructed of any suitable material with shafts through theircenters allowing them to rotate. The rollers 70 and 72 are mounted sothat the paper surface will slope downward from roller 70 to roller 72.An electromagnet 74 similar to those in FIG. 2 is mounted behind thepaper 46 and about midway between the rollers 70 and 72. After the paperhas passed around roller 72 the side having the electrostatic imagemoves across a heater 76. The heater is not a part of the invention andvarious types are known in the art so a description will not be given.

A continuous web of photosensitive paper is passed through the coronagenerator 64 which gives it a uniform electrical charge. It is thenexposed to a light image by lens 68 which dissipates the electricalcharge on the exposed areas of the paper. The paper then passes over theroller 70.

The magnetic pump 8 transports magnetic developer from the intake end 18of tube 10 to its discharge end 22. The discharge end 22 is disposed sothat the magnetic developer is ejected onto the sloping surface of thepaper at a point slightly above the electromagnet 74 and below roller70. The developer particles cascade down the sloping surface of thepaper 46 and across the electrostatic image. The combination of thedeveloper particles 80 moving across the paper and the electromagnet 74mounted behind the paper forms a magnetic developing brush which causesthe thermoplastic toner particles to adhere to the electrostatic image.

Excess magnetic developer moves down the sloping paper surface and fallsback into reservoir 20 at point 82 in the area of the roller 72. Sincethe side of the paper having the electrostatic image is facing downwardafter passing around the roller 72, excess magnetic developer will fallfrom the electrostatic image into the reservoir 20.

Finally, the developed electrostatic image passes over heater 76 whichmelts the thermoplastic toner particles and fuses them to the papersurface to form a light-fast image.

In this embodiment as in the previous one, the invention provides acontinuous circulation of the magnetic developer through theelectrophotographic machine and insures a continuing fresh supply ofdeveloper material to the magnetic brush.

What is claimed is:

1. In electrostatic printing apparatus including means for providing anelectrostatic image on a recording medium, electromagnetic developingmeans for said image and a reservoir of electromagnetic developermaterial, the improvement comprising, electromagnetic pumping means fortransporting a part of said developer material from said reservoir tosaid developing means, means for removing the unused portion of saiddeveloper material from said electrostatic image, said electromagneticpumping means including a tube of nonmagnetic material, a plurality ofelectric coils surrounding said tube, means for energizing said coils insuccession, the intake end of said tube extending into said reservoir ofelectromagnetic developer material and the discharge end adjacent to,and in operative relation with, said electromagnetic developing means,and said means for energizing said coils in succession comprisingswitching means which also momentarily energizes two adjacent ones ofsaid coils and which energizes the last one of said successivelyenergized coils for a shorter time than the others of said coils.

References Cited UNITED STATES PATENTS NORTON ANSHER, Primary ExaminerD. B. WEBSTER, Assistant Examiner

